Hanyū began existence as Hai-Ryūn Ieasomūru Jeda, an ancient being who ascended to reverence as the goddess Oyashiro-sama in Hinamizawa. She guided her clan to the Onigafuchi Swamp, later Hinamizawa, striving for human coexistence but facing discrimination due to her horns. She wed Furude Riku, the human shrine heir, and bore their daughter, Furude Ōka, founding a lineage blending human and demon heritage. To shield villagers from external demons, Hanyū sacrificed Riku, losing her capacity for visible manifestation among humans. When powerful humans seized Ōka to steal Hanyū's disease-curing medicine, Hanyū's despair twisted her into a destructive demon. Ōka bested her in combat, and Hanyū, dreading future corruption, demanded death via the sacred sword Onigari-no-ryuuou. The execution cracked one horn, establishing the first Watanagashi ceremony and birthing the Oyashiro-sama curse legend. Following physical death, Hanyū persisted as an incorporeal spirit for centuries, unseen by humans and haunted by guilt over the violence her existence ignited. She became the source of mysterious footsteps and remorseful whispers perceived by villagers suffering advanced Hinamizawa Syndrome, intensifying their paranoia. In 1983, she bonded with her descendant Furude Rika, the first since Ōka capable of seeing and interacting with her. Hanyū served as Rika's guardian and maternal figure, imparting practical skills like cooking. Their sensory link allowed shared experiences of taste or pain. Hanyū's powers enabled Rika's time-looping cycle through "Fragments" after each demise, though her waning energy confined resets to the two weeks preceding Rika's death. The crack in her horn also caused Rika's incomplete memory retention between loops. Beyond temporal manipulation, Hanyū could teleport, freeze time, project a tangible human form, and wield divine abilities including mind control or summoning the Onigari-no-ryuuou. Individuals with Level 3+ Hinamizawa Syndrome could sense her presence, though she could selectively reveal herself, demonstrated when comforting Detective Ōishi or confronting antagonist Miyo Takano. Her personality blends timidity and solemn authority. Typically, she speaks softly using verbal tics like "auu" and the masculine pronoun "boku." When enraged or invoking her goddess identity, her voice deepens resonantly, her eyes glow red or purple, and she addresses humans as "children of man." She frequently apologizes to those afflicted by Hinamizawa Syndrome, burdened by guilt over inadvertently worsening their hallucinations. Despite pessimism about escaping fate, she prioritized Rika's companionship, urging endurance through cycles over risky defiance. This dynamic sometimes provoked Rika's anger, yet Hanyū remained steadfastly loyal. In *Higurashi no Naku Koro ni Kai: Ura☆Higu*, Hanyū appears in comedic, non-canonical shorts parodying main-series scenes, depicting scenarios like advising Ōishi about insurance or Rika grabbing Mion’s breasts. Clips from these shorts appeared in *Umineko no Naku Koro ni* as in-universe television content. Later series *Gou* and *Sotsu* reveal Hanyū’s connection to the cosmic entity Eua, who identifies her as a "failure" and fragmented offshoot created when Eua’s horn was damaged. This link allowed Hanyū to temporarily harness fragment energy to defeat Eua, though her core role as Rika’s protector endured. Her relationships center on Rika, loved unconditionally despite occasional mistreatment. She shared a unique bond with Rena Ryūgū, who sensed her during past Syndrome episodes and credited her with preventing a suicide attempt. Others, like Mion’s grandmother, acknowledged her as Rika’s friend, though most remained unaware of her existence.